Apparatus and method for exhaust gas pollution reduction

ABSTRACT

A method for reducing pollution in exhaust gases and a system for treating exhaust gas are provided. The method includes the step of treating an exhaust gas stream with a treating fluid. In one application, the treating fluid is injected by spraying droplets into the exhaust gas stream. A system for treating exhaust gas includes a reagent, and a nozzle to spray the reagent into the exhaust gas stream.

FIELD OF THE INVENTION

The present disclosure relates to particulate matter pollution reductionin exhaust gases.

BACKGROUND OF THE INVENTION

Industrial exhaust gases vary significantly and typically containvolatile heavy metals, such as mercury, which are generally volatilizedfrom the raw materials and fuels and carried into the atmosphere. Forinstance, cement kiln exhaust gases typically contain oxides of carbon,sulfur, nitrogen, alkalis, excess chlorides and volatile heavy metalssuch as mercury. Mercury in both its elemental and ionic form aregenerally continually emitted through the exhaust stack in varyingconcentrations dependent upon the operation of the kiln, in-line rawmill and raw material or fuel inputs.

These gases may also be re-used for drying and heating within the inlineraw mill and then exit the process as cement kiln exhaust gas. The heavymetals within the gases may then be released to the atmosphere afterthey pass through a kiln baghouse electrostatic precipitator, or otherparticulate collection apparatus.

Typical mercury concentrations in cement kiln exhaust gases may varysignificantly and are highly dependent on the raw materials, processconditions, and fuels burned in the clinkering process at each site.Previous attempts to capture and contain mercury from cement kilnexhaust gas in both its elemental and its oxide form have generally hadmixed results. These processes may also be expensive. These processesinclude activated carbon injection, flue gas desulphurization scrubbers,and sorbent technology. Furthermore, the treatment fluid used in theseprocess may cause the creation of undesirable chemical byproducts.

Treatment processes for power plants such as those disclosed in HurleyU.S. Pat. Nos. 7,407,602, 7,771,683, and 7,776,294 are likewiseinapplicable or inappropriate to the environment of the cement kiln fora variety of reasons.

SUMMARY OF THE INVENTION

In an illustrative embodiment, a method for treating industrial exhaustgas is disclosed. The method includes providing an exhaust gas streamfrom an industrial process; providing a reagent; combining the exhaustgas stream with the reagent to create a combined stream; and removing atleast a portion of one heavy metal, such as mercury, from the combinedstream. The method may further include passing the combined streamthrough a particulate collection system and recycling the collectedparticulate for use as raw material.

In combining the exhaust gas stream with the reagent, the method mayinclude spraying the reagent into the exhaust gas stream. The method mayinclude combining the reagent with one or more solvents to create areagent solution prior to combining the exhaust gas stream with thereagent. Factors affecting the amount of reagent used or its ratio tosolvent may include the exhaust's particulate load, dispersion, exhaustgas velocity, presence and amount of metals other than mercury, and anynumber of other environmental or processing parameters. It is oftendesirable to use as little of the reagent as needed to achieve thedesired amount of heavy metal reduction.

The method may also include providing at least one of a surfactant, adispersant, and a hyperdispersant, and combining the reagent and solventwith the at least one of the surfactant, the dispersant, and thehyperdispersant prior to combining the exhaust gas stream with thereagent.

The reagent solution may further comprise one or more chelating agents.In an exemplary embodiment, the reagent solution may include a mixtureof ethylenediaminetetraacetic acid (“EDTA”) and amino tris(methylenephosphonic acid) (“ATMP”) and/or their corresponding salts.

In some embodiments, the solvent may include a diol such as propyleneglycol. Accordingly, the solvent may include a water dilution ofpropylene glycol.

In an illustrative embodiment, a method for reducing pollution in anindustrial environment is disclosed. In this embodiment, the methodincludes treating an exhaust gas stream with a treating fluid. Thetreating fluid may comprise one or more chelating agents (e.g., EDTA andATMP), a solvent such as propylene glycol, and at least one of asurfactant and a hyperdispersant.

Injecting the treating fluid may include spraying droplets of thetreating fluid into the exhaust gas stream. The treating fluid may beinjected into the exhaust gas stream at a point where the exhaust gasstream has a temperature of about 350 degrees Fahrenheit. The treatingfluid may be injected into the exhaust gas stream subsequent to a firstparticulate collection system and prior to a second particulatecollection system. The treating fluid may also be injected into a gasresonance chamber or a duct carrying the exhaust gas stream.

The treating fluid may also contain water and at least one of asurfactant and a hyperdispersant. The system and method may be adaptedso that the droplets have a size which allows the droplets to have aminimum residence time of about 1 to about 2 seconds within the exhauststream. In some applications, this minimum residence time may beachieved when the droplets have an average size of about 20 microns orgreater, and more particularly about 30 microns to about 40 microns.Longer residence times are likewise both achievable and suitable forindustrial applications, as are larger droplet sizes.

In an illustrative embodiment, a system for treating exhaust gas isdisclosed. The system includes a treating fluid; at least one nozzleconfigured to communicate with an exhaust gas stream and to spraydroplets of the treating fluid into the exhaust gas stream; and at leastone vessel fluidly connected to the nozzle and configured to store thetreating fluid.

The nozzle may be configured to spray droplets having a size configuredto allow the droplets to have a minimum residence time of about 1 toabout 4 seconds. The nozzle may be configured to spray droplets havingan average size of about 20 microns or greater.

The treating fluid may comprise a reagent containing one or morechelating agents, where the one or more chelating agents may compriseboth EDTA and ATMP. The treating fluid may include the reagent combinedwith water and/or propylene glycol. The treating fluid may also includeat least one of a surfactant, a dispersant, and a hyperdispersant.

In an illustrative embodiment, the chelating agents in the treatingfluid may sequester particulate matter (e.g., heavy metals) within theexhaust gas stream. Furthermore, in embodiments in which the treatingfluid comprises propylene glycol, the viscosity of the propylene glycolmay provide a “sticking” effect which may enhance the ability of thetreating fluid to capture particulate matter. The resulting particulatescan be collected by a particulate collection system. In someembodiments, the particulates may be transferred to storage forcontrolled metering back into a cement grinding mill and/or used as afiller material within a concrete batch plant, asphalt plant orlandfilled.

Utilization of the systems and methods disclosed herein in theapplication of the treating fluid may provide an effective way tocapture particulate pollutants in exhaust gas streams (e.g., heavymetals such as mercury) without producing undesirable byproducts whichmay occur as a result of a chemical reaction between the treating fluidand the particulate matter. Furthermore, the non-hazardous nature of thecomponents of the treating fluid may simplify on-site storage and/orinventory requirements.

These and other aspects of the disclosure may be understood more readilyfrom the following description and the appended drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

Embodiments of the disclosure are illustrated in the figures of theaccompanying drawings which are meant to be exemplary and not limiting,in which like references are intended to refer to like or correspondingparts, and in which:

FIG. 1 illustrates an embodiment of a system and method for treatingexhaust gases to reduce pollution where the treating fluid is sprayedinto a duct containing particulate matter;

FIG. 2 illustrates an embodiment of a system and method for treatingexhaust gases to reduce pollution where the treating fluid is sprayedinto a gas resonance chamber, cyclone, or additional duct containingparticulate matter;

FIG. 3 illustrates an embodiment of a system and method for treatingexhaust gases to reduce pollution where the treating fluid is sprayedinto a gas resonance chamber, cyclone, or additional duct between twoparticulate collection systems;

FIG. 4 illustrates an embodiment of a method of recycling raw materials;

FIG. 5 illustrates an embodiment of an integrated injection system andmethod for treating exhaust gases to reduce pollution;

FIG. 6 illustrates an enlarged view of one portion of the system of FIG.5 including two injection points;

FIG. 7 illustrates a top sectional view of the two injection points ofFIG. 6 ;

FIG. 8 illustrates an embodiment of a lance suitable for use in thevarious embodiments of this disclosure, including the systems of FIGS.5-7 ;

FIG. 9 illustrates a schematic view of an embodiment of a spray patternfrom the nozzles at one injection point of the system of FIGS. 5-8 ;

FIG. 10 illustrates an embodiment of fluid connections at the injectionpoint of the system of FIG. 9 ;

FIG. 11 illustrates a schematic view of an embodiment of a spray patternthrough the nozzles at another injection point of the system of FIGS.5-8 ; and

FIG. 12 illustrates an embodiment of fluid connections the injectionpoint of the system of FIG. 11 .

DETAILED DESCRIPTION OF THE INVENTION

Detailed embodiments of the systems, methods, and apparatuses forexhaust gas pollution reduction are disclosed herein; however, it is tobe understood that the disclosed embodiments are merely exemplary of thesystems, methods, and apparatuses, which may be embodied in variousforms. Therefore, specific functional details disclosed herein are notto be interpreted as limiting, but merely as a basis for the claims andas a representative basis for teaching one skilled in the art tovariously employ the systems, methods, and apparatuses for exhaust gaspollution reduction. For instance, though reference may be made toreducing pollution in exhaust gases from a cement kiln, it should beunderstood that the systems, methods, and apparatuses as describedherein may be applicable to removing pollutants from byproducts of othertypes of industrial processes.

The heavy metals, such as mercury, which are sought to be managedthrough the systems, methods, and apparatuses of the present disclosuremay be derived primarily from raw materials which are chemically alteredduring a clinker process releasing these materials into a cement kilnexhaust gas stream containing cement kiln dust, and to the atmospherethrough a kiln baghouse, electrostatic precipitator (ESP), or otherparticulate collection system. These raw materials may include calcium,silica, iron and alumina derived primarily from various forms oflimestone, clay, shale, slags, sand, mill scale, iron-rich material(IRM), pumice, bauxite, recycled glass, ashes, and similar materials.

In one illustrative embodiment, exhaust gases may be cement kiln exhaustgases which are typically passed from a kiln through one or moreprocesses, ducts, mills, cyclones, particulate collection systems suchas kiln bag houses, ESPs, or other particulate collection systems, andexit at a kiln exhaust stack. As illustrated in FIGS. 1-3 , the exhaustgas stream 22 containing particulate matter is passed from a kiln (notshown) to an exhaust gas diverter gate 24. At the diverter gate 24, allor a portion of the exhaust gas stream 22 may be passed through a duct26 and used for drying and heating within a raw mill 28, or passedthrough a bypass duct 30. As illustrated in FIGS. 1-3 , when all or aportion of the exhaust gas stream 22 is used for drying and heatingwithin the raw mill 28, the exhaust gas stream 22 passes through the rawmill 28 and a duct 32 to a raw mill cyclone or cyclone 34 located abovea kiln feed silo 36. After the exhaust gas stream 22 passes through thecyclone 34, the exhaust gas stream 22 passes through a return duct 38,which connects with the bypass duct 30.

The exhaust gas stream 22 in the bypass duct 30 may then pass throughone or more particulate collection systems 40 during which particulatesmay be collected. In some embodiments, the particulates may be used as amodified cement kiln dust (mCKD) 42. After the particulate collectionsystem(s) 40, the exhaust gas stream 22 passes through a duct 44 andexits through a kiln exhaust stack 46.

In an illustrative embodiment, the exhaust gas stream 22 is treated witha fluid, solution, or treating fluid, by injecting or spraying thetreating fluid into one or more ducts, chambers, or other processequipment carrying the exhaust gas stream 22. The treating fluid may beprovided in a fully soluble form enabling low cost application andretrofitting of existing facilities.

The treating fluid may contain a reagent containing one or morechelating agents which may sequester particulate matter in the exhaustgas stream 22. Examples of such chelating agents may include, but arenot limited to ethylenediaminetetraacetic acid (“EDTA”) and aminotris(methylene phosphonic acid) (“ATMP”). In some embodiments, thereagent may comprise multiple chelating agents. For instance, thereagent may comprise a combination of EDTA and ATMP to create asynergistic effect on capturing particulate pollutants.

The treating fluid may, in addition to or in lieu of water, comprise asolvent which may serve as a “sticking component” to further captureparticulate matter from the exhaust gas stream 22. In an illustrativeembodiment, the solvent may be a diol such as propylene glycol which maybe diluted with water in a 12-15 to 1 ratio. Accordingly, in anillustrative embodiment, the treating fluid may comprise a combinationof EDTA and ATMP in addition to propylene glycol to capture particulatepollutants through sequestration and Van der Waals interactions withoutchemically altering the particulate matter or generating ancillarychemical byproducts.

The reagent and water (or solvent) may be combined into the treatingfluid prior to injecting or spraying the treating fluid into the one ormore ducts, chambers, or other process equipment carrying the exhaustgas stream 22. For example, the reagent and water may be combined wellin advance of (e.g., one or more hours, days, weeks, months, etc. inadvance) or just prior to (e.g., one or more minutes prior to) injectingor spraying the treating fluid into the one or more ducts, chambers, orother process equipment.

Alternatively, the reagent and water may each be separately sprayed orinjected into the one or more ducts, chambers, or other processequipment carrying the exhaust gas stream 22 in a manner such that theyintersect, combine, interact or coalesce in the one or more ducts,chambers, or other process equipment to form a solution or compositionin situ, forming droplets of the solution or composition with thereagent reacting with the metal(s) in the exhaust gas stream 22 forremoval. In another variation, the treating fluid may be introduced tothe exhaust gas stream 22 by adding it to a conventional flue gasdesulfurization solution that is sprayed into a duct.

The treating fluid may also contain one or more surfactants,dispersants, and/or hyperdispersants to assist in the removal ofmetal(s) from the exhaust gas stream 22. In some embodiments, thesurfactant may be an amphoteric or zwitterionic surfactant. In oneembodiment, the surfactant, dispersant, and/or hyperdispersant iscomposed of one or more polyethylene oxide-polyethylene blockco-polymers and/or the phosphate esters thereof. When the surfactant,dispersant, and/or hyper dispersant is included, the surfactant,dispersant, and/or hyper dispersant may be provided in an amountsufficient to assist in maintaining the reaction agent or reagent in thetreating fluid prior to reaction with the metal(s), for example in anamount of about 1% or less. According to the latter case, thesurfactant, dispersant, and/or hyper dispersant is a polyethyleneoxide-polyethylene block co-polymer and the phosphate esters thereof.

In an illustrative embodiment, the reagent, water, and the one or moresurfactants, dispersants, and/or hyper dispersants may be combined intothe treating fluid prior to injecting or spraying the treating fluidinto the one or more ducts, chambers, or other process equipmentcarrying the exhaust gas stream 22. For example, the reagent, water, andthe one or more surfactants, dispersants, and/or hyper dispersants maybe combined well in advance of (e.g., one or more hours, days, weeks,months, etc. in advance) or just prior to (e.g., one or more minutesprior to) injecting or spraying the treating fluid into the one or moreducts, chambers, or other process equipment.

In an illustrative embodiment, the treating fluid is sprayed or injectedinto the exhaust gas stream 22. The treating fluid may be sprayed orinjected into the exhaust gas stream 22 through a gas resonance chamberor integrated into suitable ductwork prior to or after the kilnbaghouse, electrostatic precipitator, or particulate collection system40, and/or a flue gas desulfurization scrubber. The gas resonancechamber or ductwork is configured to form a zone which assists inbringing the particulate and the gas stream in the exhaust gas stream 22into contact with the treating fluid. In some embodiments, the treatingfluid may physically capture the metals and other particulate matterwithin the exhaust gas stream 22 by chelation and/or sequestration.

Once the exhaust gas stream 22 in the chamber or ductwork is acted uponby the treating fluid, the particulate residue is generally captureddownstream, which, depending on the particular configuration, may bewithin the existing kiln baghouse, electrostatic precipitator, in asecondary polishing baghouse, or other particulate collection system 40.In some embodiments, the captured particulate may be a dry materialreferred to as modified cement kiln dust (“mCKD”). In the case of acement kiln equipped with a flue gas desulfurization scrubber, aparticulate residue may also be captured within the scrubber as acomponent of the generated synthetic gypsum resulting in modifiedsynthetic gypsum (“mSyngyp”). The mCKD and/or the mSyngyp can then betransferred to storage for controlled metering back into a cementgrinding mill and/or used as a filler material within a concrete batchplant, asphalt plant or landfilled as non-leachable mCKD and mSyngyp. Inan illustrative embodiment, the spray or injection timing of thetreating fluid into the exhaust gas stream 22 may be aligned with theoperation of the raw mill 28, may be continuous, or may be intermittent,dependent upon the needs of the plant. In certain applications, thesystem for injecting the fluid (also referred to herein as the injectionsystem) is operated when the exhaust is more likely to exceed applicableemission limits for the heavy metals being captured. For example, incertain applications, when the raw mill 28 is not operating, the exhaustgas may be more likely to include higher concentrations of heavy metals,and the injection system may be operated suitably at that time. Othercement kiln operations may require the injection system to operate whilethe raw mill 28 is also operating, depending on the cement makingapparatus and process with which the injection system is associated, aswell as the location of such injection system.

In an illustrative embodiment, the injection system for treating exhaustgases includes a tank or other suitable vessel for storing the spray ortreating fluid, and suitable fluid connections to the exhaust gas streamto transport the fluid into operative proximity to the exhaust gasstream containing mercury and other metals to be captured. The injectionsystem includes one or more nozzles, ports, or other suitable openingspositioned so that a spray fluid is formed. Multiple nozzles at spacedlocations and with differing angular orientations generate a suitabledispersal pattern to contact the exhaust gas stream.

A system and method for treating exhaust gases to reduce pollutionaccording to an illustrative embodiment is described with reference toFIG. 1 . As illustrated in FIG. 1 , the injection system includes one ormore nozzles 48 integrated into the ductwork used to transport theexhaust gas stream 22 from the kiln (not shown). In this illustrativeembodiment, the nozzles 48 are integrated into a pre-existing duct. Thenozzles 48 are suitably positioned to communicate with bypass duct 30.The nozzles 48 are connected to a vessel 50, for storing the spray ortreating fluid, through one or more fluid connections 52, such as pipesand/or hoses. The treating fluid may be stored in the vessel 50 andtransported through the fluid connections 52 to the exhaust gas stream22 in the bypass duct 30. The treating fluid can then be sprayed orinjected into the exhaust gas stream 22.

In this embodiment, the nozzles 48 are positioned to communicate withbypass duct 30 downstream of the raw mill 28 and prior to theparticulate collection system 40. Treatment by the injection system,illustrated in FIG. 1 , occurs prior to the exhaust gas stream 22entering the one or more particulate collection systems 40. As such, theinjection system may be designed such that the inlet temperature of theduct system is hot enough to accommodate the temperature drop across theinjection system while in operation, while also meeting the operationalrequirements of the existing particulate collection system 40, baghouse,or ESP, such as an inlet temperature selected to avoid both high heatsituations (for example above 400° F.) and low dew point situations (forexample below 200° F.) which can lead to corrosion. It should beappreciated that the temperature drop across the injection system whilein operation may depend on the inlet temperature, the amount of treatingfluid being injected and other variables of the type.

In an illustrative embodiment, the treating fluid injected or sprayedthrough the nozzles 48 has a large enough droplet size allowing thetreating fluid to intercept the cement kiln exhaust gas stream for aminimum of about 1-2 seconds either intermittently or on a continualbasis while the treating fluid is being injected and the reactionoccurs. However, it should be appreciated that longer residence times orinterception times can be used and may be preferred based upon theparticular application.

Treatment by the injection system, illustrated in FIG. 1 , occurs priorto the exhaust gas stream 22 entering the one or more particulatecollection systems 40. As such, in some embodiments, particulates arecaptured as a dry residual material resulting in the modified cementkiln dust (mCKD) 42. This mCKD 42 may no longer be soluble in terms ofleachate in soils, cement or concrete as the captured mercury and othermetals are now permanently insoluble. The mCKD 42 may be used as one ofthe additional materials inserted into a finish mill in thecement-making process, which is described in further detail below withreference to FIG. 4 .

While, the injection system including nozzles 48 is integrated orinstalled in a preexisting duct (e.g., the bypass duct 30), it should beappreciated that the injection system including nozzles 48 can beinstalled in one or more newly added, modified, or preexisting ducts atany number of different locations. For example, the injection system maybe installed or placed to contact the exhaust gas stream 22 upstream ofthe raw mill 28, downstream of the raw mill 28, in the bypass duct 30,in the return duct 38, downstream of the particulate collection system40, upstream of the particulate collection system 40, or in one or moreexisting, modified, or additional ducts associated therewith.

When an injection system, similar to the integrated injection systemillustrated in FIG. 1 is integrated or installed after, or downstreamof, the particulate collection system 40, kiln baghouse or ESP, theinjection system may be designed such that the inlet temperature of theinjection zone is hot enough to accommodate the temperature drop acrossthe injection zone while in operation while meeting the requirements ofa secondary particulate collection system, such as illustrated in FIG. 3. This integrated injection system may be configured to spray dropletshaving a large enough droplet size to allow the droplets to interceptthe exhaust gas stream for about 1-2 seconds or longer, eitherintermittently or on a continual basis while the treating fluid is beinginjected and the reaction occurs. The resulting particulate may becarried directly into the secondary particulate collection system andcontained as a concentrated residue.

The ductwork associated with the injection system may be pre-existing ornewly installed as part of the injection system. The ductwork associatedwith the injection system, whether pre-existing or new, may optionallybe treated with a polymer or may require additional ducting, chambers,or other modifications to its geometry to insure the treating fluid orchemical remains in an active form for a length of time suitable totreat the cement kiln exhaust gas stream as intended before entering theparticulate collection system.

In other embodiments, additional ductwork, chambers (such as gasresonance chambers), and/or modifications to the pre-existing ductworkmay be used in creating a suitable treatment or injection system.Another system and method for treating exhaust gases to reduce pollutionaccording to an illustrative embodiment is described with reference toFIG. 2 . As illustrated in FIG. 2 , the injection system includesadditional duct work and is installed or placed upstream of theparticulate collection system 40. The additional ductwork includes afirst duct 54, a resonance chamber or a cyclone 56, and a second duct58. In this illustrative embodiment, the first duct 54 is connected tothe bypass duct 30, the resonance chamber 56 is connected to the firstduct 54, and the second duct 58 is connected to the resonance chamber 56and to the inlet of the particulate collection system 40. Thus, theexhaust gas stream 22 flows from the bypass duct 30 through the firstduct 54, through the resonance chamber 56, and through the second duct58 into the particulate collection system 40.

In addition to the additional ductwork, the injection system includesone or more nozzles 60 suitably positioned to communicate with theresonance chamber 56. In this illustrative embodiment, the nozzles 60are connected to a vessel 62 for storing the spray or treating fluidthrough one or more fluid connections 64, such as pipes and/or hoses.The treating fluid is typically stored in the vessel 62 and transportedthrough the fluid connections 64 to the exhaust gas stream 22 in theresonance chamber 56. The treating fluid can then be sprayed or injectedinto the exhaust gas stream 22.

In this embodiment, the nozzles 60 are positioned to communicate withresonance chamber 56 downstream of the raw mill 28 and prior to theparticulate collection system 40. Treatment by the injection system,illustrated in FIG. 2 , occurs prior to the exhaust gas stream 22entering the one or more particulate collection systems 40. Again, inthis embodiment, the injection system may be designed such that theinlet temperature of the resonance chamber 56 is hot enough toaccommodate the temperature drop across the resonance chamber 56 whilein operation, while also meeting the operational requirements of theexisting particulate collection system 40, baghouse, or ESP, such as aninlet temperature selected to avoid both high heat situations (forexample above 400° F.) and low dew point situations (for example below200° F.) which can lead to corrosion.

In an illustrative embodiment, the treating fluid injected or sprayedthrough the nozzles 60 has a large enough droplet size to allow thetreating fluid to intercept the cement kiln exhaust gas stream for about1-4 seconds or longer, either intermittently or on a continual basiswhile the reagents are being injected and the reaction occurs. However,it should be appreciated that longer residence times or interceptiontimes can be used and may be preferred based upon the particularapplication. As in the previous embodiments, particulates may becaptured as a dry residual material resulting in the modified cementkiln dust (mCKD) 42. The mCKD 42 may be used as one of the additionalmaterials inserted into a finish mill in the cement-making process,which is described in further detail below with reference to FIG. 4 .

Another system and method for treating exhaust gases to reduce pollutionaccording to an illustrative embodiment is described with reference toFIG. 3 . As illustrated in FIG. 3 , the injection system includesadditional duct work and is installed or placed between two particulatecollection systems 40 a and 40 b. The additional ductwork includes afirst duct 66, a gas resonance chamber or a cyclone 68, and a secondduct 70. In this illustrative embodiment, the first duct 66 is connectedto the outlet of the particulate collection system 40 a, the resonancechamber 68 is connected to the first duct 66, and the second duct 70 isconnected to the resonance chamber 68 and to the inlet of theparticulate collection system 40 b. Thus, the exhaust gas stream 22flows from the particulate collection system 40 a through the first duct66, through the resonance chamber 68, and through the second duct 70into the particulate collection system 40 b.

As in the previous embodiments, the injection system includes one ormore nozzles 72 suitably positioned to communicate with the resonancechamber 68. In this illustrative embodiment, the nozzles 72 areconnected to a vessel 74 for storing the spray or treating fluid throughone or more fluid connections 76, such as pipes and/or hoses. Thetreating fluid is typically stored in the vessel 74 and transportedthrough the fluid connections 76 to the exhaust gas stream 22 in theresonance chamber 68. The treating fluid can then be sprayed or injectedinto the exhaust gas stream 22.

In this embodiment, the nozzles 72 are positioned to communicate withthe resonance chamber 68 downstream of the particulate collection system40 a and prior to the particulate collection system 40 b. Treatment bythe injection system, illustrated in FIG. 3 , occurs after theparticulate collection system 40 a and prior to the particulatecollection system 40 b. In this embodiment, similar to the others, theinjection system may be designed such that the inlet temperature of theresonance chamber 68 is hot enough to accommodate the temperature dropacross the resonance chamber 68 while in operation, while also meetingthe operational requirements of the particulate collection system 40 b,baghouse, or ESP, such as an inlet temperature selected to avoid bothhigh heat situations (for example above 400° F.) and low dew pointsituations (for example below 200° F.) which can lead to corrosion.

In this illustrative embodiment, similar to the others, the treatingfluid injected or sprayed through the nozzles 72 has a large enoughdroplet size to allow the treating fluid to intercept the cement kilnexhaust gas stream for a minimum of about 1-4 seconds, eitherintermittently or on a continual basis while the reagents are beinginjected and the reaction occurs. However, it should be appreciated thatlonger residence times or interception times can be used and may bepreferred based upon the particular application.

The resulting particulate may be carried directly into the particulatecollection system 40 b and contained as a concentrated residue 78. Thisresidue 78 may no longer be a threat in terms of leachate in soils,cement or concrete as the captured mercury and other metals are nowpermanently insoluble. The residue 78 may be highly concentrated withheavy metals and may require additional testing for disposal or may useas a process addition within a cement mill. Additionally, theparticulates captured by the particulate collection system 40 a, (CKD80) may be used alone or in combination with the residue 78 as one ofthe additional materials inserted into a finish mill in thecement-making process, which is described in further detail below withreference to FIG. 4 .

While the systems described above have been installed at certainlocations, it should be appreciated that the systems can be installed atany number of different locations. For example, the system may beinstalled or placed to contact the exhaust gas stream upstream ordownstream of the raw mill, upstream and/or downstream of one or moreparticulate collection systems, or between one or more existing ductsassociated therewith. Treatment may thus be accomplished through any ofa variety of pre-existing ducts, a gas resonance chamber, a dryscrubber, or through other suitable zones, either prior to or after theone or more particulate collection systems, including the cement kilnbaghouse, electrostatic precipitator, or a flue gas desulfurizationscrubber.

In the illustrative embodiments disclosed herein, the spray injectiontiming may be aligned with the operation of the raw mill 28 or may becontinuous dependent upon the needs or goals of the plant to reduceemissions or comply with any applicable regulations. As shown in FIGS. 1and 2 , utilizing the injection system prior to the existing particulatecollection system 40 may reduce investment cost and operating cost whencontrasted with a wet scrubber, dry scrubber application or activatedcarbon injection.

It should be appreciated that in one or more of the embodimentsdisclosed herein there is no requirement for a ‘Polishing Baghouse’. Theinjection system may be installed in-line with an existing kiln baghouseand the material collected may simply be segregated during periods whenit is in operation. A separate dust storage and metering system may beincluded to hold the material until it can be put back into the finishmills on a controlled basis. The collected material can successfully beutilized as a process addition within the cement mills without anydanger of releasing the captured mercury. Once the residual material iscaptured in concrete, it may not re-release as it is substantiallypermanently bound in its stable natural form, unlike what generallyresults from the use of activated carbon or sorbent technology. Thecaptured mercury is contained in its stable natural form. It may notre-release into the air or leach into the soil unless it is physicallyprocessed again through a kiln or combustion system.

Any of the embodiments disclosed herein may include a dust storage andmetering system for containment of the captured mCKD and re-introductionof the mCKD to the cement milling process to be used in furtherproduction steps or recycling of the mCKD back into the kiln processafter removal of the entrained heavy metals such as mercury. The mCKDcan be transferred directly to a storage silo for controlled meteringback into a cement grinding mill, as a process addition, and/or useddirectly as a filler material within a concrete batch plant, asphaltplant or landfilled as non-leachable mCKD.

A method of recycling the mCKD and other raw materials according to anillustrative embodiment is described with reference to FIG. 4 . Aclinker 82 produced in the kiln is cooled and may be transferred to astorage silo 84 for controlled metering into one or more finish mills86. Additionally, gypsum 88 may be transferred to a storage silo 90 forcontrolled metering into the finish mill 86. The gypsum 88 may be usedas a process addition to the finish mill 86, replacing, for example,about 5.0% of the total raw materials being utilized. In an illustrativeembodiment, the gypsum 88 is a modified synthetic gypsum (mSyngyp)captured by a flue gas desulfurization scrubber.

As illustrated in FIG. 4 , a dust storage and metering system forcontainment of the captured mCKD 92 and re-introduction of the mCKD 92to the cement milling process is included. The mCKD 92 can betransferred directly to a storage silo 94 for controlled metering intothe finish mill 86, as a process addition. The mCKD 92 may be used as aprocess addition to a finish mill 86, replacing, for example, up toabout 5.0% of the total raw materials being utilized. It should beappreciated that the mCKD may make up a larger or smaller percentage ofthe total materials as understood by those skilled in the art in view ofthe present disclosure.

The mCKD 92 is ultimately bound within the Portland cement and used asconcrete, with the resultant material being stabilized andnon-leachable. As illustrated in FIG. 4 , a dust storage and meteringsystem is used to hold the mCKD 92 until it can be put back into thefinish mill 86 on a controlled basis. As described above, the mCKD 92may be substantially permanently bound in its stable natural form, assuch; the collected mCKD 92 can successfully be utilized as a processaddition within the cement mill without any danger of releasing thecaptured mercury.

Installation of the mCKD dust storage and metering system may allow theplant to effectively manage the mCKD material 92 and test it in advanceof recycling, re-using or disposing.

In another illustrative embodiment, a continual emission monitoringsystem capable of accurately measuring mercury and other heavy metalsfor monitoring of system performance may be implemented as part of thesystem.

An example of an integrated injection system according to anillustrative embodiment is described with reference to FIGS. 5-13 . Withreference to FIG. 5 , the integrated injection system is installed in acement plant 96. The plant 96 produces an exhaust gas stream 98 from akiln (not shown), which flows from the kiln downstream through adowncomer duct 102. At the base of the downcomer duct 102 there is adrop out box 104, which is designed to allow any solidified material tofall out of the exhaust gas stream 98, separating it from the gases andparticulate matter that continue through the ductwork. Connected to theoutlet of the drop out box 104 is a duct 106, which carries the exhaustgas stream 98 downstream to a particulate collection system 108. Theexhaust gas stream 98 flows through the particulate collection system108 into a duct 110, which carries the exhaust gas stream 98 downstreamto an exhaust stack 112 through which the exhaust gas stream 98 exitsinto the atmosphere.

Referring to FIGS. 5 and 6 , the integrated injection system includes afirst injection point 114 installed in the downcomer duct 102 and asecond injection point 116 installed in the duct 106. The integratedinjection system is located upstream of the particulate collectionsystem 108. As such, and similar to the previously describedembodiments, particulates are captured in the particulate collectionsystem 108 as a dry residual material resulting in modified cement kilndust (mCKD) 118. This mCKD 118 may no longer be soluble in terms ofleachate in soils, cement or concrete as the captured mercury and othermetals are now permanently insoluble. Again, as in previous versions,the mCKD 118 may be used as one of the additional materials insertedinto a finish mill in the cement-making process, such as described abovewith reference to FIG. 4 .

A schematic top down view of the first and second injection points 114and 116 according to an illustrative embodiment is described withreference to FIG. 7 . As illustrated in FIG. 7 , first ports 120 areinstalled in the downcomer duct 102 at the first injection point 114,and second ports 122 are installed in the duct 106 at the secondinjection point 116. As illustrated, the downcomer duct 102 has adiameter of about twenty (20) feet and there are nine (9) first ports120 around the circumference of the downcomer duct 102. The duct 106 hasa diameter of about eleven and a half (11.5) feet and there are nine (9)second ports 122 around the circumference of the duct 106. However, itshould be appreciated that the number of first ports 120 and the numberof second ports 122 may be smaller or larger than nine (9), dependentupon the particular application and sizes of the ducts.

Referring now to FIGS. 7-11 , first ports 120 and second ports 122 arefour inches in diameter, and installed at radially spaced locationsaround the circumference of downcomer duct 102 and the duct 106,respectively. The ports are aligned in parallel to each other. Dependingon the particular application, it should be appreciated that the ports120, 122 may be smaller or larger than four inches in diameter, ports120 need not be of the same dimension as ports 122, and the spacing andorientation may be varied. The ports 120, 122 are designed to penetratethe sidewall of the downcomer ducts 102, 106 for insertion of lances 128a-r of spray nozzles into the downcomer ducts 102, 106 as discussedbelow.

In this illustrative embodiment, lances having one or more nozzlespositioned thereon inserted into corresponding ones of the ports 120,122. Each of the ports 120, 122 can hold a lance. However, it should beappreciated that not all of the ports 120, 122 are required to have acorresponding lance inserted therein during operation. The lances mayhave a length that allows the lance to extend from the particular portinto which the lance is received across at least a portion of the duct.It should be appreciated that the lances may have differing lengths andmay extend varying distances across the duct. For example, the lancesmay extend substantially across the duct from corresponding ports, ormay be sized or otherwise configured to extend a portion of the wayacross the duct from such ports.

As seen in FIGS. 7, 9, and 11 , cross supports 132 and 136, fitted withsaddles for each lance (not shown), may extend below and across thelances of a corresponding duct and engage the underside or topside ofsuch lances to support them. The cross supports 132 and 136 extend at anangle (perpendicular in this version) to corresponding lances and ismounted through corresponding ports 124, 126.

An embodiment of one of lances 128 a-r according to an illustrativeembodiment is further described with reference to FIG. 8 . Asillustrated in FIG. 8 , a lance 128, such as one of lances 128 a-rdescribed below, has one or more nozzles 130 installed thereon. In thisembodiment the lance 128 is made of stainless steel. However, it shouldbe appreciated that the lance 128 may be made of other materials, suchas but not limited to iron, aluminum, polymers, and other materials ofthe type. In this embodiment, the nozzles 130 are configured to dispersedroplets of the treating fluid. The droplet size should be large enoughto allow the droplets to exist long enough and react with the metal(s),such as ionic and elemental mercury, within the exhaust gas stream. Inthis embodiment, the droplets may have an average size of about 20-40microns, and more particularly an average size of about 30-40 microns.The droplet size of about 30-40 microns is designed allow the dropletsto reside in the exhaust gas stream for a minimum of about 1-2 secondswhen the temperature at the injection point is on average about 350° F.However, the droplet sizes can be made to vary, for example the dropletsmay have an average size of about 20 microns or larger, dependent uponthe exhaust gas temperature, treating fluid concentration, waterpressure, actual cubic feet per minute, particulate dust load andmercury concentrations, and other factors. For example, it should beappreciated that a higher temperature may be associated with a largerdroplet size, such as about 70 to 90 microns (though this is not anupper limit on suitable droplet size), and a lower temperature may allowfor a smaller droplet size to be used.

A schematic view of a spray pattern through the nozzles 130 within thedowncomer duct 102 at injection point 114 is illustrated and describedwith reference to FIG. 9 . As illustrated in FIG. 9 , there are nine (9)lances 128 a-i, equally spaced, each having one or more nozzles 130 (asindicated by the circular patterns) and inserted into nine of the firstports 120. In this embodiment, the lances 128 a-i are supported by thecross support 132 that extends between ports 124. The cross support 132may be fitted with saddles for the lances 128 a-i to support the lances128 a-i as the lances 128 a-i extend across the duct 102.

As illustrated in FIG. 9 , the nozzles 130 (as indicated by the circularpatterns) have a cone-shaped spray pattern with a round shaped impactarea. However, it should be appreciated that nozzles having differingshaped spray patterns and impact areas may be used.

In this embodiment, the lances 128 a and 128 i each have one (1) nozzle130, the lances 128 b and 128 h each have four (4) nozzles 130, thelances 128 a, 128 c, and 128 g each have five (5) nozzles 130, and thelances 128 d and 128 f each have six (6) nozzles 130. The spraypatterns, illustrated by the circular patterns, of the nozzles 130 coverabout 90% of the total cross sectional area of the downcomer duct 102.However, it should be appreciated that a different arrangement or numberof nozzles, smaller, larger, or different spray patterns may be used,and that the amount of coverage of the total cross sectional area of thedowncomer duct 102 may be varied so as to be a higher or smallerpercentage.

Similarly, a schematic view of a spray pattern through the nozzles 130within the duct 106 at injection point 116 is illustrated and describedwith reference to FIG. 11 . As illustrated in FIG. 11 , there are nine(9) lances 128 j-r, equally spaced, each having one or more nozzles 130(as indicated by the circular patterns) and inserted into nine of thesecond ports 122. In this embodiment, the lances 128 j-r are supportedby the cross support 136 that extends between ports 126. The crosssupport 136 may be fitted with saddles for the lances 128 j-r to supportthe lances 128 j-r as the lances 128 j-r extend across the duct 106.

As illustrated in FIG. 11 , the nozzles 130 (as indicated by thecircular patterns) have a cone-shaped spray pattern with a round shapedimpact area. However, it should be appreciated that nozzles havingdiffering shaped spray patterns and impact areas may be used.

In this embodiment, the lances 128 j and 128 r each have one (1) nozzle130, the lances 128 k-m and 1280-q each have four (4) nozzles 130, andthe lance 128 n has five (5) nozzles 130. The spray patterns,illustrated by the circular patterns, of the nozzles 130 cover about 90%of the total cross sectional area of the duct 106. However, it should beappreciated that any number of nozzles having smaller or larger spraypatterns may be used to cover a higher or smaller percentage of thetotal cross sectional area of the duct 106.

As illustrated, with reference to FIGS. 8-10 , the nozzles 130 arefluidly connected to one or more vessels for storing the treating fluid,via one or more of the lances 128 a-i, through one or more fluidconnections 134, such as pipes and/or hoses. The treating fluid isstored in the vessel and transported (for example via a pump) throughthe fluid connections 134, through the one or more lances 128 a-i andexits through the nozzles 130 within the downcomer duct 102. Thetreating fluid then contacts the exhaust gas stream 98 within thedowncomer duct 102. Similarly, as illustrated with reference to FIGS. 8,11, and 12 , the nozzles 130 on the lances 128 j-r at the secondinjection point 116 in the duct 106 are fluidly connected to a vessel,containing the treating fluid, via one or more fluid connections 138,such as pipes and/or hoses.

The integrated injection system, described above with reference to FIGS.5-12 , can be implemented in cement plant 96 (FIG. 5 ) to remove mercuryfrom exhaust gas stream 98. The temperature of the exhaust gas stream 98varies dependent upon operation of an inline raw mill and/or the kilnconditions. In this illustrative embodiment, the temperature at theinlet to the downcomer duct 102, which is upstream of the raw mill,varies from about 600 to 800° F. Temperatures at the inlet to theparticulate collection system 108 typically range from about 240-300° F.to protect the particulate collection system 108. When the raw mill isoperating, the exhaust gas stream 98 loses heat as it passes through theraw mill to dry out the raw materials while grinding is taking place.When the raw mill is not operating, it is generally necessary to lowerthe temperature of the exhaust gas stream 98 by using a high pressurewater spray in the downcomer duct 102. This typically cools the exhaustgas stream 98 down to about 325-395° F. at the inlet to the particulatecollection system 108 to protect the particulate collection system 108.The particulate loading of exhaust gas stream 98 can be as high as 20tons per hour (tph) through the downcomer duct 102 and is not dependenton raw mill operation. The exhaust gas stream 98 gas volume can vary by4,000,000 standard cubic feet per hour (sal) during operation due totemperature fluctuations and process conditions.

In an illustrative embodiment, the treating fluid contains a reagent andsolvent. The reagent may be a chelating agent mixture comprising EDTAand ATMP. The solvent may contain a water dilution of propylene glycol.The reagent and solvent is injected when the raw mill is off and thetemperature is reduced to about 350° F. at the exit of the duct 106. Asdescribed above, the first injection point 114 is installed in thedowncomer duct 102, prior to the drop out box 104, and the secondinjection point is installed in the duct 106, after the drop out box104. The treating fluid is injected through the nozzles 130 at a rate ofabout fifteen (15) gallons per minute, a pressure of about 45 psi, andhas an average droplet size of about 30-40 microns. The droplet size ofabout 30-40 microns is designed to allow the reagent to reside in theexhaust gas stream 98 long enough to come into contact with andsequester the particulates (e.g., heavy metal) within the exhaust gasstream 98 by chelation and/or physical interactions with the propyleneglycol. In this embodiment, the 30-40 micron droplets reside for aminimum of about 1-2 seconds within the exhaust gas stream 98 having atemperature of about 350° F., on average, before evaporating.Additionally, the 30-40 micron droplets prevent the reagent frombuilding up on a downstream preheater ID fan (not shown) that is presentin the cement plant 96. Under these conditions, a smaller droplet maynot provide the droplet enough life to allow the reaction to occur, anda larger droplet may carry to the preheater ID fan where it maycontribute to buildup and vibration leading to fan failure.

While the systems and methods disclosed herein are described withreference to certain embodiments, it should be appreciated thatindustrial system configurations may vary greatly and thus locations andconfigurations of the treatment system relative to the exhaust gasstream may be correspondingly varied to suit the particular industrialsystem. It should also be appreciated that any of the embodimentscontemplated herein may or may not require one or more secondaryparticulate removal systems, depending on the particular applications.

Depending on the individual kiln operation, raw materials, and fuels,the systems disclosed herein may run only intermittently, on an asneeded basis, or they may run substantially continually to achievedesired reduction goals, including the injection of treating fluid 100%of the time. In most cases, the highest period of mercury emissionrelates to when the in-line vertical mill or raw mill is off or whenthere is a temperature discrepancy in the kiln baghouse, ESP, or otherparticulate collection system. Accordingly, the treatment process may beconfigured to run during such off-line periods, or it may be triggeredto run in response to any number of parameters, such as time, theexceeding of certain emission thresholds, running emission averages,measurements of gas constituents, and other parameters of the type. Eachsystem may be tailored to each cement kiln based on actual emissionmodeling, raw materials, costs, and any number of other operational,emission, or functional parameters.

In an illustrative embodiment, the duct(s), chambers, or other treatmentzones associated with the treatment system are configured to addresstemperature drops as the exhaust stream travels downstream. For example,as disclosed above, in certain embodiments, the treatment zone (duct,chamber, cyclone, etc.) may be selected or configured so that the inlettemperature of the treatment zone is hot enough to accommodate thetemperature drop across the zone while in operation, while meeting theoperational requirements of a downstream baghouse, ESP, or otherparticulate collection system. Such an inlet temperature avoids bothhigh heat situations and low dew point situations which lead tocorrosion.

The systems, methods, and processes disclosed herein have beenidentified, adapted to, and designed for the cement industry. In oneform, the systems, methods, and processes disclosed herein may provide alower capital cost, lower operating cost, and most importantly reducedmercury emission levels.

It should be appreciated that a version of this technology can also beapplied to cement-making plants equipped with a wet scrubber or alreadydesigned for use of activated carbon injection. Retrofitting of existingfacilities is expressly among the possible configurations.

It should also be understood that, using the systems and methodsdisclosed herein, mercury is captured regardless of where it isgenerated during the cement-making process, without the need forre-heating. The systems and methods disclosed herein may allow thecement plants to use a greater variety of raw materials without fear ofexceeding any applicable emission limits for mercury or other heavymetals captured as described in this disclosure. Depending on the volumeof residual material generated, the portion which cannot be utilized asa process addition will have to be disposed of, but this is expected tobe a minor volume in the overall context.

While the above description relates generally to mercury capture, itshould be appreciated that the systems, methods, processes, andtechnology disclosed herein may be modified to capture hexavalentchromium and a variety of other metals and emission hot points.

The matter set forth in the foregoing description and accompanyingdrawings is offered by way of illustration only and not as a limitation.While the systems, methods, and apparatuses for cement kiln exhaust gaspollution reduction have been described and illustrated in connectionwith certain embodiments, many variations and modifications will beevident to those skilled in the art and may be made without departingfrom the spirit and scope of the disclosure. The disclosure is thus notto be limited to the precise details of methodology or construction setforth above as such variations and modification are intended to beincluded within the scope of the disclosure.

1. A method for treating exhaust gas streams from an industrial process,the method comprising: providing an exhaust gas stream; providing areagent comprising one or more chelating agents; combining the exhaustgas stream with the reagent to create a combined stream; and removingparticulates comprising at least a portion of one heavy metal from thecombined stream by forming a particulate residue containing the heavymetal in non-leachable form.
 2. The method of claim 1, wherein the oneor more chelating agents comprises a mixture ofethylenediaminetetraacetic acid and amino tris (methylene phosphonicacid).
 3. A system for treating exhaust gas streams from an industrialprocess, the system comprising: a treating fluid comprising a reagentcomprising one or more chelating agents; at least one nozzle configuredto communicate with an exhaust gas stream; a particulate collectionsystem; and wherein said at least one nozzle is configured to injectsaid treating fluid into said exhaust gas stream to form a combinedstream before entering the particulate collection system and wherein theparticulate collection system is configured to separate particulatescomprising at least a portion of one heavy metal from the combinedstream by forming a particulate residue containing the heavy metal innon-leachable form.
 4. The system of claim 3, wherein said treatingfluid further comprises at least one selected from the group of asurfactant, a dispersant, and a hyperdispersant.
 5. The system of claim3, wherein the treating fluid comprises a solvent comprising propyleneglycol.